Chiastolite

Chiastolite is a variety of andalusite. It is noted for distinctive cross-shaped black inclusions of graphite. Chiastolite crystals have been pseudomorphically altered by a mixture of muscovite, paragonite and margarite. The calcium rich margarite tends to form along the graphite rich crosses or bands within the chiastolite. Mineralogically the occurrence is important because all three white mica phases are present in an equilibrium assemblage. Source Wikipedia.

The meaning of the name Chiastolite comes from the Greek word "chiastos" meaning cruciform or crosswise. Chiastolite has a long association with healing and protection.